Back to EveryPatent.com
| United States Patent |
5,202,715
|
|
Matsubara
|
April 13, 1993
|
Plate member for use as material of light shielding blades
Abstract
A laminated plate member having a thickness of 60 to 120 .mu.m and used as
a material of focal plane shutter blades or iris blades of a camera has an
intermediate layer made from a material composed of uni-directionally
oriented continuous (long) or short carbon fibers and a matrix resin
enveloping the carbon fibers, the material having a resin content ranging
from 50 to 60 wt % when the carbon fibers are long fibers and 60 to 75 wt
% when the fibers are short fibers, and surface layers on both sides of
the intermediate layer, each surface layer being made from a material
composed of a matrix resin enveloping long carbon fibers uni-directionally
oriented in a direction substantially orthogonal to that of the carbon
fibers in the intermediate layer, the material of the surface layers
having a resin content ranging from 30 to 45 wt %.
| Inventors:
|
Matsubara; Takashi (Tokyo, JP)
|
| Assignee:
|
Nikon Corporation (Tokyo, JP)
|
| Appl. No.:
|
905137 |
| Filed:
|
June 23, 1992 |
Foreign Application Priority Data
| Dec 07, 1989[JP] | 1-318244 |
| Sep 18, 1990[JP] | 2-247917 |
| Current U.S. Class: |
396/452; 396/458; 396/483; 396/493; 396/505 |
| Intern'l Class: |
G03B 009/40 |
| Field of Search: |
354/226,245-250
359/227,233,234,235,236
428/113,288,408
|
References Cited
U.S. Patent Documents
| 4482231 | Nov., 1984 | Kato et al. | 354/246.
|
| 5025278 | Jun., 1991 | Matsubara | 354/246.
|
| Foreign Patent Documents |
| 0394996 | Oct., 1990 | EP.
| |
| 8633679 | Feb., 1987 | DE.
| |
| 3919770 | Dec., 1989 | DE.
| |
| 59-61827 | Apr., 1984 | JP.
| |
| 62-199439 | Sep., 1987 | JP.
| |
| 63-17435 | Jan., 1988 | JP.
| |
Primary Examiner: Gellner; Michael L.
Assistant Examiner: Blankenship; Howard B.
Attorney, Agent or Firm: Shapiro and Shapiro
Parent Case Text
This is a continuation of application Ser. No. 621,887 filed Dec. 4, 1990,
now abandoned.
Claims
What is claimed is:
1. A light-shielding blade having a thickness of 60 to 120 .mu.m and
comprising a laminate of at least three blade-layers of carbon fiber
reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented long carbon fibers enveloped in
matrix resin and with resin content ranging from 50 to 60 wt %; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer
and with resin content ranging from 30 to 45 wt %.
2. A shutter blade having a thickness of 60 to 120 .mu.m and comprising a
laminate of at least three blade-layers of carbon fiber reinforced resin
sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented long carbon fibers enveloped in
matrix resin and with resin content ranging from 50 to 60 wt %; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer
and with resin content ranging from 30 to 45 wt %.
3. A light-shielding blade having a thickness of 60 to 120 .mu.m and
comprising a laminate of at least three blade-layers of carbon fiber
reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented short carbon fibers enveloped in
matrix resin and with resin content ranging from 60 to 75 wt %; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer
and with resin content ranging from 30 to 45 wt %.
4. A shutter blade having a thickness of 60 to 120 .mu.m and comprising a
laminate of at least three blade-layers of carbon fiber reinforced resin
sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented short carbon fibers enveloped in
matrix resin and with resin content ranging from 60 to 75 wt %; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer including at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer
and with resin content ranging from 30 to 45 wt %.
5. A light-shielding blade comprising a laminate of at least three
blade-layers of carbon fiber reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented long carbon fibers enveloped in
matrix resin; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer;
and
wherein the sheet material of said one layer of said intermediate
blade-layer has a higher resin content than the sheet material of the
respective said one layer of each said surface blade-layer.
6. A light-shielding blade according to claim 5, wherein the sheet material
of the respective said one layer of each said surface blade-layer has a
resin content of 30 to 45 wt %.
7. A shutter blade comprising a laminate of at least three blade-layers of
carbon fiber reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented long carbon fibers enveloped in
matrix resin; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer;
and
wherein the sheet material of said one layer of said intermediate
blade-layer has a higher resin content than the sheet material of the
respective said one layer of each said surface blade-layer.
8. A shutter blade according to claim 7, wherein the sheet material of the
respective said one layer of each said surface blade-layer has a resin
content of 30 to 45 wt %.
9. A light-shielding blade comprising a laminate of at least three
blade-layers of carbon fiber reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented short carbon fibers enveloped in
matrix resin; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer;
and
wherein the sheet material of said one layer of said intermediate
blade-layer has a higher resin content than the sheet material of the
respective said one layer of each said surface blade-layer.
10. A light-shielding blade according to claim 9, wherein the sheet
material of the respective said one layer of each said surface blade-layer
has a resin content of 30 to 45 wt %.
11. A shutter blade comprising a laminate of at least three blade-layers of
carbon fiber reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with uni-directionally oriented short carbon fibers enveloped in
matrix resin; and
surface blade-layers on both sides of said intermediate blade layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented in a direction substantially orthogonal to that
of said carbon fibers in said one layer of said intermediate blade-layer;
and
wherein the sheet material of said one layer of said intermediate
blade-layer has a higher resin content than the sheet material of the
respective said one layer of each said surface blade-layer.
12. A shutter blade according to claim 11, wherein the sheet material of
the respective said one layer of each said surface blade-layer has a resin
content of 30 to 45 wt %.
13. A light-shielding blade comprising a laminate of at least three
blade-layers of carbon fiber reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with short carbon fibers enveloped in matrix resin; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer having at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented.
14. A light-shielding blade according to claim 13, wherein the short carbon
fibers of said one layer of said intermediate blade-layer are
uni-directionally oriented in a first direction, and the long carbon
fibers of said one layer of each surface blade-layer are uni-directionally
oriented in a second direction substantially orthogonal to said first
direction.
15. A shutter blade comprising a laminate of at least three blade-layers of
carbon fiber reinforced resin sheet material, including:
an intermediate blade-layer having at least one layer made from sheet
material with short carbon fibers enveloped in matrix resin; and
surface blade-layers on both sides of said intermediate blade-layer, each
said surface blade-layer including at least one layer made from sheet
material with long carbon fibers enveloped in matrix resin and
uni-directionally oriented.
16. A shutter blade according to claim 15, wherein the short carbon fibers
of said one layer of said intermediate blade-layer are uni-directionally
oriented in a first direction, and the long carbon fibers of said one
layer of each surface blade-layer are uni-directionally oriented in a
second direction substantially orthogonal to said first direction.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plate member for use as a material of
light shielding blade members which are required to move at a high
velocity, such as focal plane shutter blades or lens shutter blades of a
camera.
2. Related Background Art
In general, it is desirable to operate a light-shielding blade at a high
velocity with a small force, and with minimal flexing of the blade. This
requires a light-shielding blade that is lightweight and that possesses
high strength and rigidity.
To meet the foregoing requirement, a plate member for use as a material of
light-shielding blades has been proposed which has a laminate construction
including a reinforced-resin intermediate layer composed of a resin matrix
with uni-directionally oriented continuous (long) carbon fibers, and
reinforced-resin surface layers composed of a resin matrix with continuous
carbon fibers uni-directionally oriented in a direction substantially
orthogonal to the direction of the fibers in the intermediate layer, the
light-shielding member having a total thickness of 60 to 120.mu.. This
type of plate member is disclosed, for example, in Japanese Patent
Application Laid-Open No. 59-61827 U.S. Pat. No. 4,482,231, Japanese
Patent Application Laid-Open No. 62-199439 and Japanese Patent Application
Laid-Open No. 63-17435.
Obviously, the layers forming this plate member are arranged in
plane-symmetry in the thickness direction. In addition, each of the
intermediate and surface layers may be a laminate layer composed of a
plurality of thin reinforced resin sheets. In general, 20 to 50 blades are
formed by cutting or punching from this plate member, such that, in each
blade the longitudinal direction of the carbon fibers of the intermediate
layer is substantially orthogonal to the longitudinal axis of the blade.
The light-shielding blades thus formed are lightweight and superior in
hardness and rigidity, and are actually used in cameras having a high
shutter release speed of 1/8000 second.
The light-shielding blade thus formed suffers from disadvantages due to its
small thickness which usually ranges between 60 and 120.mu.. The first
problem is that the plate member as the blank of the light-shielding blade
generally exhibits a large thickness variation. The second problem is that
the plate member is inferior in flatness, i.e., that the plate member is
warped or distorted. The third problem is that the light-shielding blade
formed by punching or cutting also is inferior in flatness.
FIG. 1 is an illustration of a vertical-running type focal plane shutter in
assembled state, wherein the light-shielding blades formed by the
above-described process are used as a first blade 31, a second blade 39, a
third blade 40, a fourth blade 41 and a fifth blade 42.
Arms 34 and 35 are rotatably connected to pins 32, 33 provided on the first
blade 31. The arms 34, 35 are rotatable about shafts 37, 38 provided on a
shutter base plate 36. The pins 32, 33 and the shafts 37, 38 are arranged
in a parallelepiped quadrilateral form, so that the first blade 31
translationally moves in the vertical direction of the aperture 46 in
accordance with rotation of the arms 32, 33. However, the second blade 39,
the third blade 40, the fourth blade 41 and the fifth blade 42 are moved
in a manner different from that of movement of the first blade 31. More
specifically, a pin 43 provided on the first blade 31 is rotatably
connected to the second blade 39, while a pin 45 provided on an arm 44
rotatably supported by a shaft 37 engages with a cam groove 39a formed in
the base portion of the second blade 39. Consequently, the motion of the
second blade 39 is determined by the movement of the pin 45 and the
contour of the cam groove 39a, through the action of the pin 43. The third
blade 40 is rotatably carried by the shaft 38 and a cam groove 40a
engaging with the pin 45 is provided on the base portion thereof. The
fourth and fifth blades 41 and 42 are also rotatably carried by the shaft
38 and are provided with cam grooves 41a and 42a for engagement with the
pin 45. The pin 45 also is rotatably connected to arm 34 which is
rotatably supported by the shaft 37, so as to rotate together with the arm
44 which rotates about the shaft 37. The cam grooves 39a, 40a, 41a, and
42a are arranged such that the blades are developed to cover the aperture
46 when the first blade 31 is positioned above the aperture 46 as viewed
in the Figure, whereas, when the first blade 31 is retracted to the
underside of the aperture 46, all the blades are superposed. In this
arrangement, the third to fifth blades 40 to 42 rotate about the center of
the shaft 38 as if forming a fan or a sector. In general, a focal plane
shutter device of the kind described includes a pair of the described
group of blades. One of the blade groups serves as shutter opening blades,
while the other serves as shutter closing blades.
The focal plane shutter device of the kind described, employing blades made
from the conventional plate member,tends to suffer from problems in regard
to connection between the driving system and the blades due to inferior
flatness of the plate member and due to local reductions in strength
caused by presence of micro-cracks and cavities in the plate material. In
addition, the appearance of the blades and applicability of DL (dry
lubricant) are also impaired.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to overcome the
above-described problems of the prior art.
The present inventor conducted extensive research to determine the causes
of these problems. As a result of this effort, it was discovered that with
the conventional plate member, in which both the intermediate and surface
layers have resin contents as small as 30 to 45 wt %, the small resin
content in the intermediate layer leads to the creation of defects, such
as micro-cracks and cavities, as well as to inferior flatness.
As a result of a further study, the present inventors have found that the
above-described problems of the prior art can be overcome by increasing
the resin content of the intermediate layer to 50 to 60 wt % when the
resin is used in combination with continuous (long) fibers and to 60 to 75
wt % when used together with short fibers, without increasing the resin
content of the surface layers. Thus, the inventors have found also that
the desired light-shielding blades can be obtained even if short fibers
are used in place of conventional continuous or long fibers in the
intermediate layer,
provided that the short fibers are uni-directionally oriented.
According to the present invention, there is provided a laminated plate
member having a thickness of 60 to 120.mu. for use as a material of
light-shielding blades, comprising: an intermediate layer having at least
one layer made from sheet material with uni-directionally oriented
continuous or short carbon fibers enveloped in matrix resin and with resin
content ranging from 50 to 60 wt % when said carbon fibers are continuous
fibers and 60 to 75 wt % when said fibers are short fibers; and surface
layers on both sides of the intermediate layer, each surface layer having
at least one layer made from sheet material with continuous carbon fibers
enveloped in matrix resin and uni-directionally oriented in a direction
substantially orthogonal to that of the carbon fibers in said one layer of
the intermediate layer and with resin; content ranging from 30 to 45 wt %.
The reinforced resin from which the intermediate and surface layers are
formed is composed of uni-directionally oriented continuous carbon fibers
and matrix resin enveloping such fibers. The fiber, however, may be short
fibers in the case of the intermediate layer. Preferably, a prepreg sheet
formed by impregnating carbon fibers with a precursor of the matrix resin
is used as the green material.
The prepreg sheet is formed by impregnating reinforcement fibers with a
thermosetting resin liquid, e.g., uncured liquid of an epoxy resin or
unsaturated polyester, which is a precursor of the matrix resin, and
transforming the resin liquid to B stage in which the resin has been cured
to eliminate fluidity but is still curable finally by application of heat.
The plate member of the present invention can be formed by preparing a
plurality of prepreg sheets each being about 10 to 60.mu. thick,
sandwiching at least one prepreg sheet as an intermediate layer between at
least two prepreg sheets as the surface layers, such that the the
longitudinal axes of the surface fibers in the sheet of the intermediate
layer and those of the carbon fibers in the two sheets of the surface
layers are substantially orthogonal to each other, and such that these
layers are arranged in a plane-symmetry in the thicknesswise direction,
and applying heat and pressure to the sandwich structure so as to cure the
resin.
The intermediate layer and each of the surface layers may be formed from a
plurality of prepreg sheets stacked and laminated with their carbon fibers
oriented in the same direction or substantially at right angles. For
instance, the plate member may have one upper surface layer made from a
single prepreg sheet, an intermediate layer composed of two prepreg sheets
superposed one on the other with their carbon fibers oriented in the same
direction, and one lower surface layer composed of a single prepreg sheet,
the upper and lower surface layers having their carbon fibers oriented in
the direction orthogonal to the carbon fibers of the prepreg sheets
forming the intermediate layer.
The carbon fibers used in the intermediate layer may be short carbon fibers
with lengths preferably ranging between 1 and 30 mm and more preferably
between 5 and 15 mm.
Both the continuous (long) and short carbon fibers preferably have
diameters of 3 to 10.mu..
In order to obtain sufficiently high light-shielding effect and surface
lubricating power, carbon black may be added to the prepreg composition as
desired, at a ratio of 5 to 15 wt % to the resin liquid (solid content 100
wt parts). Preferably, the carbon black has a mean particle size of
0.07.mu. or less. The addition of the carbon black may be made only to the
prepreg sheets of the surface layers or only to the prepreg sheet or
sheets of the intermediate layer. Different characteristics are obtainable
by selective addition of the carbon black to the prepreg layers.
The plate material of the invention can be obtained by subjecting the
laminate of the prepreg sheets to heat-pressing. A black coating (dry
lubricant application) may be effected in this step for the purposes such
as improvement in the light-shielding effect, reduction in the surface
reflectivity, improvement in the appearance and improvement in the surface
lubricating property. The thickness of the coating film is preferably 0.1
to 10.mu.. In order to eliminate any risk of warping or distortion of the
plate member, the thickness of the coating layer is preferably selected to
range between 0.1 to 3 .mu.m.
By cutting or punching the thus obtained plate member into light-shielding
blades of a predetermined configuration, it is possible to produce 20 to
50 light-shielding blades at a time. The cutting or punching is conducted
such that the carbon fibers in at least one sheet used in the intermediate
layer are oriented orthogonally to the longitudinal axis of the blade,
i.e., such that the longitudinal axes of these fibers are substantially
orthogonal to the longitudinal axis of the blade. The black coating may be
applied to each piece of the light-shielding blade at this point, rather
than during the heat-pressing stage as noted above.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of a vertical-running type focal plane shutter in
assembled state;
FIG. 2 is a schematic vertical sectional view of Example 2 of a plate
member for the invention for use as a material of light-shielding blades;
and
FIG. 3 is a schematic vertical sectional view of Example 3 of a plate
member of the invention for use as a material of light-shielding blades.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be fully described hereinafter with respect to its
preferred embodiments. It is to be understood, however, that the described
embodiments are only illustrative and do not limit the scope of the
invention, which is defined in the appended claims.
Referring to FIGS. 2 and 3, numeral 1 denotes continuous (long) carbon
fibers, 2 denotes a matrix resin, 3 denotes surface layers, 4 denotes
carbon black, 5 denotes short carbon fibers, 6 denotes a matrix resin and
7 denotes an intermediate layer.
EXAMPLE 1
(1) Prepreg sheets A of 20 to 40.mu. thick were prepared by enveloping, in
an epoxy resin as a matrix resin, uni-directionally oriented continuous
carbon fibers of 6 to 7.mu. in diameter. The resin content of the prepreg
sheet A was 35 to 45 wt %.
(2) Prepreg sheets B of 10 to 50.mu. thick were prepared by enveloping, in
an epoxy resin as a matrix resin, uni-directionally oriented short carbon
fibers of 6 to 7.mu. in diameter and 1 to 30 mm in length. The resin
content of the prepreg sheet B was 60 to 75 wt %. This sheet B could be
produced by centrifugal lifting method which makes use of a paper making
process.
(3) A multiplicity of plate members of 60 to 120.mu. thick were produced by
using the prepreg sheets. More specifically, each plate member was formed
by interposing one prepreg sheet B forming an intermediate layer between a
pair of prepreg sheets A forming surface layers, in a plane-symmetrical
form such that the direction of the longitudinal axes of the sheet B was
orthogonal to the direction of the longitudinal axes of the carbon fibers
in the sheets A. Thus, the directions of the longitudinal axes of the
carbon fibers of both sheets A were the same. The thus formed sandwich
structure was then subjected to a pressure of 5 to 15 kg/cm.sup.2 at
130.degree. C. and was left for 1 to 2 hours so that the epoxy resin was
cured. Subsequently, the structure was gradually cooled down to room
temperature, whereby the plate member was formed.
The plate members thus formed were examined for any thickness variation and
warp, and the ratio of the number of the plate members having acceptable
levels of flatness to the total number of the plate members was
determined. This ratio will be referred to as "first yield", hereinafter.
(4) 20 to 50 light-shielding blades for a focal plane shutter device were
produced by press punching from one of the plate members having acceptable
levels of flatness. The punching was conducted such that the direction of
the longitudinal axes of the carbon fibers of the intermediate layer were
orthogonal to the longitudinal axis of the light-shielding blade.
The thus obtained light-shielding blades were examined for thickness
variation and warp, and the ratio of the number of the light-shielding
blades having acceptable levels of flatness, to the total number of the
blades was determined. This ratio will be referred to as "second yield".
(5) Black coating film with dry lubricant, 4.mu. in thickness, was formed
on each side of each of the light-shielding blades having acceptable
levels of flatness. Formation of the black coating film on the blade
member often causes internal strain to be developed so as to warp the
blade. Therefore, the light-shielding blades with black coating film were
examined for any warp and the ratio of the number of the light-shielding
blades with acceptable levels of flatness to the total number of the
blades with black coating film was determined. This ratio will be referred
to as "third yield", hereinafter. The first to third yields thus
determined are shown in Table 1.
COMPARISON EXAMPLE 1
Three prepreg sheets A used in Example 1 were superposed such that the
direction of the longitudinal axes of the carbon fibers in the
intermediate sheet was orthogonal to the directions of longitudinal axes
of the carbon fibers of the two outer sheets A. Using this structure,
plate members, light-shielding blades and black-coated light-shielding
blades were produced in the same manner as Example 1, and the first to
third yields of were determined by the same procedure as Example 1. The
results are shown in Table 1.
TABLE 1
______________________________________
Example 1 Comparison Example 1
______________________________________
First yield (%)
Approx. 100% Approx. 90%
Second yield (%)
Approx. 80 to 100%
Approx. 50 to 70%
Third yield (%)
Approx. 90% Approx. 90%
Total Approx. 72 to 90%
Approx. 41 to 57%
______________________________________
EXAMPLE 2
Prepreg sheets A' were prepared to have the same construction as the
prepreg sheets A used in Example 1 except that 10 wt % of carbon black,
having a mean particle size of 0.01.mu. or less, was added per 100 weight
parts. Using these prepreg sheets A', plate members, light-shielding
blades and black-coated light-shielding blades were produced in the same
manner as Example 1.
EXAMPLE 3
Prepreg sheets B' were prepared to have the same construction as the
prepreg sheets B used in Example 1 except that 10 wt % of carbon black,
having a mean particle size of 0.01.mu. or less, was added per 100 weight
parts. Using these prepreg sheets B', plate members, light-shielding
blades and black-coated light-shielding blades were produced in the same
manner as Example 1.
EXAMPLE 4
Plate members were produced by sandwiching two prepreg sheets B of Example
1 between a pair of prepreg sheets A of Example 2, such that the direction
of the longitudinal axes of the carbon fibers in the intermediate sheets B
was orthogonal to the direction of the longitudinal axes of the carbon
fibers in the outer surface sheets A'. Thus, the sandwich structure was
formed by four sheets arranged in plane-symmetry in the thickness
direction, so that the resulting plate member has an intermediate layer
composed of a pair of sheets B. Using the thus obtained plate members,
light-shielding blades and black-coated light-shielding blades were
produced in the same manner as Example 1.
EXAMPLE 5
Prepreg sheets B" of 10 to 50.mu. thick were prepared by enveloping
uni-directionally oriented continuous carbon fibers of a mean diameter of
6 to 7.mu. in an epoxy resin as a matrix resin. The resin content was 50
to 60 wt %. Plate members, light-shielding blades and black-coated
light-shielding blades were produced in the same manner as Example 1
except that the prepreg sheets B" were used in place of the prepreg sheets
B.
The black-coated light-shielding blades of Examples 1 to 5 were subjected
to a durability test in high-speed camera shutters. The high-speed
shutters produced from these black-coated light-shielding blades could
withstand more than 400,000 shutter releasing cycles, thus proving
satisfactory high-speed stability and high-speed running characteristics.
The intermediate layer can be formed of three or more prepreg sheets B. In
such a case, it is not always necessary that all these prepreg sheets
constituting the intermediate layer have an equal resin content, although
it is essential that these three or more prepreg sheets are arranged in
plane-symmetry. When a plurality of prepreg sheets are used to form the
intermediate layer, these prepreg sheets maybe assembled such that the
directions of orientation of carbon fibers in these sheets are orthogonal
to each other.
As has been described, according to the present invention, it is possible
to obtain a plate member for use as a material of light-shielding blades
with a high level of flatness at a high yield, i.e., with high values of
the aforesaid first to third yields. Consequently, the cost of production
of light-shielding blades can be reduced remarkably despite the use of
prepreg sheets which are generally expensive due to use of carbon fibers.
In addition, since a high level of flatness is obtainable in conjunction
with reduced thickness of the plate member, the weight of the
light-shielding blade is reduced, which significantly contributes toward
realization of super-high-speed shutter blades which operate at a very
high speed of 1/12000 second or higher.
Top